1. Field of the Invention
The present invention relates generally to the area of sample taking and more particularly to an apparatus for removing multiple sample volumes of a material from a moving conveyor.
2. Description of the Related Art
In processing mined materials, for example, coal, the coal is moved along a series of conveyors through and between various processing stages and stations. Further, as the coal moves through different processing points, at each point, the coal will have a unique combination of physical characteristics that make it suitable for particular applications. Other applications may require additional processing, for example, additional crushing, sizing, washing and other step to improve quality. As the coal is processed to a point that it is suitable for a particular application, some of the coal is diverted for final processing and testing prior to transportation.
For each application, the coal is tested against quality standards associated with that application. Therefore, as coal intended for a particular application is conveyed, a primary sample volume of the coal is periodically removed from the conveyor. That primary sample is further conveyed to another station where a generally smaller secondary sample volume is periodically taken. Those secondary samples are collected and analyzed as a representation of the composite of the total load.
The sample quantities and sampling frequency associated with each application, or use, of the coal are determined by industry standards which, for example, may be set by the American Society of Testing Materials (ASTM). After the coal samples are collected, the samples are then tested to determine qualitative variables such as sulfur content, ash, BTU content, etc., to confirm that the coal complies with the standards established for its intended application or use. The samples and test results are often forwarded to the customer so that the customer can compare the sample analysis against the actual shipment of coal received.
A total shipment of coal may be up to generally 10,000 tons or 100 rail cars. While having a composite sample of all 10,000 tons is helpful, all 10,000 tons are not identically homogeneous with regard to their qualitative characteristics. Therefore, if there is a discrepancy found in the sample, it is very difficult to associate that discrepancy with a particular quantity of the total 10,000 ton load. Therefore, it is the practice to obtain multiple samples from any particular load. For example, a first sample may be taken that represents a composite of all 10,000 tons or 100 rail cars comprising the total quantity of coal sold. Further, additional samples may be taken which represent a composite sample of a fraction of the total load such as, for example, 500 tons or 5 rail cars. Therefore, if qualitative discrepancies are found, they may be more easily associated with a particular portion of the total load.
Various mechanisms currently exist for removing samples of material, such as coal, from a moving conveyor. The assignee of the present invention has marketed several different coal samplers. For example, one sampler has a sampling scoop connected to a unidirectional rotating drive shaft coupled through a gear drive to an AC motor. A mechanical brake holds the scoop in a park, or home, position at which the centerline of the scoop is above the axis of rotation at a 10 o'clock position. In response to a sample command, the brake releases the drive, and the AC motor rotates the scoop one complete revolution. As the scoop passes transversely over the moving conveyor, a predetermined volume of coal is collected and pushed off the conveyor into a collection chute. The bottom edge of the scoop is curved at a radius equal to the distance from the axis of rotation to the bottom edge, and the moving conveyor is curved to match the curvature of the bottom edge of the scoop.
Other coal sampling mechanisms are known such as, for example, those available from J. B. Long, of Knoxville, Tenn. They market a sampler which is movable bidirectionally but not through a full revolution. The sampling scoop is held by a brake in a first home position located approximately at the 10 o'clock position on a first side of the conveyor. The scoop is pneumatically driven and pivots across the conveyor to a second home position located approximately at the two o'clock position adjacent the other side of the conveyor. That pivoting motion pushes a coal sample off the other side of the conveyor. A mechanical brake also holds the scoop at the second home position. When the scoop is pivoted in the opposite direction to the 10 o'clock position first home position, it pushes a coal sample off the first side of the conveyor. If only a single sample is required, the scoop is pivoted in one direction for example, from the ten o'clock first home position to the two o'clock second home position. In order to return the scoop to the 10 o'clock first home position, the sampling scoop must be lifted vertically, it is then pivoted from above the two o'clock second home position to a position above the ten o'clock first home position. Therefore, the pivoting motion does not interfere with coal traveling on the conveyor. When above the 10 o'clock first home position, the sampling scoop is then moved vertically downward to the first home position.
The above devices have the disadvantage of having to use a brake to hold the scoop at the home positions. One of the devices requires additional mechanisms to lift and lower the scoop in order to provide a unidirectional operation to collect a single composite of samples. In addition, pneumatic devices are relatively slow which means the time between samples is relatively long.
An AC motor drive has a disadvantage in that it is less tolerant to a high sample rate requiring a high frequency of direction reversals.